This application claims the benefit of Korean Application No. 98-32889, filed Aug. 13, 1998, in the Korean Patent Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an actuator for an optical pick-up, and more particularly, to an actuator for an optical pick-up which increases a sensitivity that is a value for displaying a frequency characteristic in the actuator and a method of rolling a driving coil thereof.
2. Description of the Related Art
In general, an optical pick-up for scanning a light beam on a surface of an optical disk through an object lens and detecting a light beam reflected from the disk is installed in an optical recording and reproducing apparatus such as an optical disk player.
The optical pick-up includes a semiconductor laser, an optical lens, and an optical diode for converting an optical signal of the reflected light beam into an electrical signal, and an actuator. The optical pick-up was first used in the audio field for devices such as a CD player and has become an essential part for products using an optical disk, such as an optical magnetic disk player and a video CD player.
Recently, the optical pick-up has become very small. Therefore, the optical pick-up is sometimes called an optical head. There are primarily two types of optical heads; a separated type in which a semiconductor laser, a beam splitter, and a photodetector are fixed and a portion on which an object lens actuator is loaded is driven; and an integrated type in which all parts including an object lens actuator and optical parts are loaded on one base and all parts are moved together.
In order to reproduce information of high quality using such an optical pick-up, the focus of the light beam on the optical disk should be accurately adjusted and the irradiated light beam should accurately follow a track formed on the optical disk.
In general, the operation of vertically moving the object lens to control the focal distance is called focusing. An operation of moving the object lens so that the light (optical) beam is accurately scanned along each track of the optical disk is called tracking.
Therefore, the optical pick-up includes an actuator for supporting the object lens and performing focusing and tracking operations.
FIG. 1 is a perspective view of a conventional actuator for an optical pick-up. FIG. 2 is a plan view of the conventional actuator for the optical pick-up shown in FIG. 1. FIG. 3 is a left side view of the conventional actuator for the optical pick-up shown in FIG. 1. FIG. 4 is a front view of the conventional actuator for the optical pick-up shown in FIG. 1.
The conventional actuator for the optical pick-up includes a base 1, a holder 2 fixed to the base 1, a bobbin 4 for holding an object lens 3, a suspension (wire springs) 5 for connecting the bobbin 4 to the holder 2, and magnetic driving means for moving the bobbin 4 in the direction of the track or the focus, as shown in FIGS. 1 and 2.
The magnetic driving means includes a focus coil 6 rolled around the bobbin 4, tracking coils 7a through 7d in which tracking coils 7a and 7b are rolled at opposite ends of a first side surface of the bobbin 4 and the tracking coils 7c and 7d are rolled at opposite ends of a second side surface of the bobbin 4 opposite the first side, at an outside portion of the focus coil 6, and a pair of permanent magnets 8a and 8b. Namely, as shown in FIGS. 3 and 4, a focus coil 6 and tracking coils 7a and 7c are separately rolled (in FIG. 4, tracking coils 7a and 7b are shown). Here, the tracking coils 7a and 7b are rolled at opposite ends of a first side surface of the bobbin 4 so as to face the permanent magnet 8a and the tracking coils 7c and 7d are rolled at opposite ends of a second side surface of the bobbin 4 so as to face the permanent magnet 8b. The tracking coils 7a through 7d are positioned at the outside portion of the focus coil 6. A pair of external yokes 9a and 9b installed on the base 1 are respectively attached to the permanent magnets 8a and 8b (see FIG. 1). A pair of internal yokes 10a and 10b fixed to the base 1 guide the bobbin 4 according to the magnetic flux.
In the actuator for the optical pick-up constructed as mentioned above, when current is applied to the focus coil 6 rolled around the bobbin 4 and the tracking coils 7a through 7d respectively rolled around the opposite sides of the bobbin 4, an electromagnetic force is generated by the current and the permanent magnets 8a and 8b according to Fleming""s left hand rule. According to the direction to which the electromagnetic force operates, the bobbin 4 connected to the holder 2 installed in the base 1 by a suspension (wire springs) 5 is guided by the internal yokes 10a and 10b and is vertically or horizontally moved. Here, the force of the permanent magnets 8a and 8b is formed in the direction toward the ground. Accordingly, the object lens 3 loaded into the bobbin 4 performs the focusing and tracking operations.
According to a method of rolling a driving coil including the focus coil 6 and the tracking coils 7a through 7d by the conventional technology, the size of the permanent magnets should be large in order to improve the sensitivity by narrowing the distance between the focus coil and the permanent magnets.
Also, when the distance between each permanent magnet and the driving coil is wide, a portion in which the distribution of the magnetic flux is uniform becomes narrow. Accordingly, an imbalance of force is generated when the driving portion of the actuator is moved in the directions for tracking and focusing. Thus, the actuator is tilted, causing improper operation thereof.
To solve the above problem, it is an object of the present invention to provide an actuator for an optical pick-up, which is not improperly tilted when the driving portion of the actuator moves.
It is another object of the present invention to provide a method of rolling a driving coil in an actuator for an optical pick-up, to prevent improper tilting of the optical pick-up during tracking and focusing operations.
Accordingly, to achieve the above and other objects of the present invention, there is provided an actuator for an optical pick-up including a bobbin for holding an object lens, a suspension for connecting the bobbin to a holder, the actuator including a pair of permanent magnets respectively positioned near opposite sides of the bobbin, a plurality of tracking coils with pairs of the tracking coils rolled on opposite side surfaces of the bobbin and opposing the permanent magnets, a focus coil rolled around the bobbin and the plurality of tracking coils, wherein the plurality of tracking coils and focus coil receive current to move the optical pick-up through interaction with the permanent magnets. A strong force is generated by narrowing a distance between the permanent magnets and the focus coil based upon the focus coil being rolled around the bobbin and the tracking coils.
To further achieve the above and other objects of the present invention, there is provided a method of rolling a driving coil in an actuator for an optical pick-up including a bobbin for holding an object lens, the driving coil including a pair of permanent magnets, a plurality of tracking coils and a focus coil to move the bobbin in directions of tracking and focusing, the method including the steps of rolling the tracking coils with pairs of the tracking coils on opposite side surface of the bobbin, and rolling the focus coil around the bobbin and the plurality of tracking coils.